1) Less ambition would have meant fewer Gnome 3 usability regressions. So, yes, that's probably a good assumption.
2) No, Gnome 3 is not very usable to regular Gnome 2 users. We're talking about regular people, people who tend to dislike relearning how to do simple things. If kernel devs are ranting about how difficult it is to adopt the Gnome 3 way, just imagine how Bob the Middle Manager is fairing. Or Aunt Tillie. :) (and if you think I'm hard on Gnome 3, you should hear my non-techy wife talk about it...)
3) I do see some existing Gnome users howling in pain. I do not see Gnome 3 attracting "everyone else". If you have evidence that there's a silent surge of non-Gnome-users queuing up to use Gnome 3 then please, by all means, do share. I'd love to see it.
I love removing code as much as anyone. It truly is one of the pleasures of programming. But most of the Gnome 3 pain seems to be coming from its UI changes. That has very little to do with deprecation and almost everything to do with design.
I find Gnome 3 to be a really good start too. With some refinement, it could be truly impressive, far better than Gnome 2. Today, though, it's just not ready for the distros to be deploying by default.